Although you can use either for measuring lengths in metric units, a vernier caliper has greater precision than a meter stick. You can use a meter stick for quick measurements of objects ranging from about 5 to 95cm. Technicians and craftspeople use vernier calipers to precisely gauge objects typically smaller than 16cm, or about 6 inches.
Meter sticks have decimetre, centimetre and millimetre markings, so measurements with them are accurate to the nearest millimetre. A standard vernier caliper can make measurements down to 1/20 millimetre. A special calibrated scale on the caliper, called the Vernier scale, has markings that let you accurately determine tenths of a millimetre or hundredths of an inch. Professional calipers with a mechanical dial or electronic display can make measurements with accuracies of a hundredth of a millimetre or one thousandth of an inch.
You use the calipers by closing the outside jaws on an object. When you can move the jaws no further, you can make an accurate measurement. With a meter stick, as with a ruler, you have to judge the ends of the object with your eyes. This is not difficult for parts with rectangular features and right angles, but you can more accurately measure round, tapered or irregular items with the caliper.
In addition to measuring the outside length of an object, the Vernier caliper has inside jaws to measure things like the inside diameter of a hole. The flat parts of the inside jaws face out to rest against the inner circumference of the object. The calipers have a depth probe that protrudes from the end of the instrument. You can use this to measure the depth of holes and other penetrations. As with the inside and outside jaws, the depth probe measures by solidly contacting the bottom of the hole.